Controllable magnetic bearing apparatus and method for determining a machine type of a magnetic bearing

ABSTRACT

A rolling element in a stationary state as surrounded by magnetic bearings is moved until it abuts against a protective bearing, and thereby a mean value of movement spans S is determined. A machine type is determined based on a fact that the mean value of movement spans varies depending upon the types of machine bodies, and then the setting of control parameters is made. In this manner, a control unit of the magnetic bearing is adapted for multiple types of machine bodies.

TECHNICAL FIELD

The present invention relates to a controllable magnetic bearingapparatus and a method for determining a machine type of a magneticbearing.

BACKGROUND ART

The controllable magnetic bearing apparatus consists of a machine bodyincluding a rolling element and magnetic bearings, and a control unitfor controlling the machine body. There are plural types of machinebodies so that control parameters vary depending upon the machine types.Accordingly, there has been a need for providing each control unit incorrespondence to each type of machine body.

In order to provide each control unit in correspondence to each type ofmachine body, multiple types of control units must be fabricated on asmall-lot basis. This not only imposes inconvenience but also makes itimpossible to reduce costs through mass production.

In view of the foregoing, the present invention has an object to providea controllable magnetic bearing apparatus having a control unitapplicable to multiple types of machine bodies. It is another object ofthe present invention to provide a method for determining a machine typeto apply the control unit to any of the multiple types of machinebodies.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, a controllable magneticbearing apparatus sensing a position of a rolling element supported by amagnetic bearing and controlling the position thereof, the apparatuscomprises: means for moving the rolling element in a stationary state ina predetermined direction to determine an amount of movement thereof toa movement limit; and means for determining a machine type of themagnetic bearing based on the amount of movement and setting controlparameters (Claim 1).

In the controllable magnetic bearing apparatus thus arranged, the amountof movement of the rolling element is determined by moving the rollingelement in a stationary state to the movement limit. The machine type isdetermined based on a fact that the amount of movement varies dependingupon the machine types and then, the setting of control parameters ismade. Accordingly, a common control unit can be applied to the multipletypes of machine bodies.

In accordance with the present invention, a controllable magneticbearing apparatus sensing a position of a rolling element supported by amagnetic bearing and controlling the position thereof, the apparatuscomprises: means for moving the rolling element in a stationary state inplural directions to determine respective amounts of movement of therolling element to respective movement limits; means for determining amean amount of movement based on the amounts of movement; and means fordetermining a machine type of the magnetic bearing based on the meanamount of movement and setting control parameters (Claim 2).

In the controllable magnetic bearing apparatus thus arranged, determinedis the mean amount of movement of the rolling element when the rollingelement in a stationary state is moved to the movement limits in theplural directions. Subsequently, the machine type is determined based ona fact that the mean amount of movement varies with each machine type,so as to set the control parameters. Accordingly, a common control unitcan be applied to multiple types of machine bodies. In addition, thedetermination of the machine type is highly reliable because thedetermination is based on the mean amount of movement.

In accordance with the present invention, a method for determining amachine type of a magnetic bearing comprises: the steps of moving arolling element supported by a magnetic bearing from a rest position toplace on one side of a first radial axis for determining an amount ofmovement thereof to a movement limit; then moving the rolling element toplace on one side of a second radial axis for determining an amount ofmovement thereof to a movement limit; then moving the rolling element toplace on the other side of the first radial axis for determining anamount of movement thereof to a movement limit; then moving the rollingelement to place on the other side of the second radial axis fordetermining an amount of movement thereof to a movement limit; operatinga mean amount of movement based on the amounts of movement; anddetermining a machine type of the magnetic bearing based on the meanamount of movement and setting control parameters (Claim 3).

In the method for determining the machine type of the magnetic bearing,the mean amount of movement is found from the amounts of movement of therolling element, which, initially being in a stationary state, issequentially moved to each of the movement limits in each of thedifferent directions. The machine type is determined based on the factthat the mean amount of movement varies with each machine type. Then,the setting of control parameters is made. Accordingly, a common controlunit can be applied to multiple types of machine bodies. Thedetermination of the machine types is highly reliable because thedetermination is based on the mean amount of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing a method of machine type determinationtaken by a controllable magnetic bearing apparatus according to oneembodiment of the present invention;

FIG. 2 is a plan view showing the positional relationship between aninside-diameter circle of a protective bearing and a rolling elementmovable in a range inscribed by the circle;

FIG. 3 is a diagram showing the rolling element of FIG. 2 internallytouching a +Y side of the inside-diameter circle;

FIG. 4 is a diagram showing the rolling element of FIG. 2 internallytouching a +X side of the inside-diameter circle;

FIG. 5 is a diagram showing the rolling element of FIG. 2 internallytouching a −Y side of the inside-diameter circle:

FIG. 6 is a diagram showing the rolling element of FIG. 2 internallytouching a −X side of the inside-diameter circle;

FIG. 7 is a diagram showing each position of the center of and eachamount of movement of the rolling element when the rolling element issequentially moved to each of movement limits thereof;

FIG. 8 is a diagram showing each position of the center of and eachamount of movement of the rolling element when the rolling element issequentially moved to each of movement limits thereof, in a case wherean initial position of the center of the rolling element is out of theorigin of the X-Y coordinates;

FIG. 9 is a vertical sectional view showing a machine body of thecontrollable magnetic bearing apparatus;

FIG. 10 is a horizontal sectional view showing the above machine body;

FIG. 11 is a block circuit diagram of the above controllable magneticbearing apparatus;

FIG. 12 is a block diagram showing only a portion of the arrangement ofthe controllable magnetic bearing apparatus that is involved in thecontrol of radial position; and

FIG. 13 is a block diagram showing only a portion of the arrangement ofthe controllable magnetic bearing apparatus that is involved in thecontrol of axial position.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 9 is a vertical sectional view showing a machine body 1 of acontrollable magnetic bearing apparatus according to one embodiment ofthe present invention, and FIG. 10 is a horizontal sectional viewthereof.

The machine body 1 is of a vertical construction wherein a rollingelement 3 in the form of a vertical shaft rotates within a cylindricalcasing 2. In the following description, an axial direction of therolling element 3 is defined as Z direction and respective directionsorthogonal to the Z direction, as seen in the figure, are defined as Xdirection and Y direction.

Besides the casing 2 and rolling element 3, the machine body 1 furtherincludes an axial magnetic bearing 4, a radial magnetic bearing 5, anaxial displacement sensor 6, a radial displacement sensor 7, a motor 8,and a protective bearing 9.

The axial magnetic bearings 4 are disposed above and below a flangedportion 3 a of the rolling element 3 as sandwiching the flanged portiontherebetween, thereby axially supporting the rolling element 3 in anoncontact fashion. The radial magnetic bearings 5 are disposed at twoplaces on Z-axis thus forming two groups, each of which consists of fourradial magnetic bearings equally spaced by 90° around the rollingelement 3. The radial displacement sensors 7 are disposed at the samecircumferential positions as the radial magnetic bearings 5 in closeadjacency thereto along the Z direction, thus forming two groups offour. The axial displacement sensor 6 is disposed opposite to an axialend portion 3 b of the rolling element 3. The motor 8 is mounted to aninside wall of the casing 2 for rotating the rolling element 3 at highspeeds. The protective bearings 9 are arranged in paired relation forlimiting movable ranges of the rolling element 3 with respect to theaxial and radial directions, as well as for providing contact supportfor the rolling element 3 in case the magnetic noncontact support forthe rolling element 3 may be disabled. A radial clearance and an axialclearance between the protective bearing 9 and the rolling element 3 areof given values determined according to the type of the machine body 1.

FIG. 11 is a block circuit diagram showing connection between themachine body 1 of the above arrangement and a control unit 11 forming,in combination with the machine body, the controllable magnetic bearingapparatus.

The control unit 11 includes a sensor circuit 12, a magnetic-bearingdrive circuit 13, an inverter 14, a DSP board 15 and a serialcommunication board 21. The DSP board 15 is provided with a DSP 16 as adigital signal processor, a ROM 17 connected thereto, a flash memory 18as a nonvolatile storage device, an A/D converter 19 and a D/A converter20.

A personal computer 22 disposed at place remote from the control unit 11is connected to the serial communications board 21 of the control unit11.

Output signals from the axial displacement sensor 6 and radialdisplacement sensors 7 are inputted to the DSP 16 via the sensor circuit12 and A/D converter 19. On the other hand, the DSP 16 provides controlof the axial magnetic bearings 4 and radial magnetic bearings 5 via theD/A converter 20 and magnetic-bearing drive circuit 13, thereby allowingthe rolling element 3 to be supported in the noncontact fashion ascontrolling the position of the rolling element 3. The DSP 16 alsocontrols the rotation of the motor 8 via the inverter 14.

The ROM 17 stores a processing program and the like to be performed inthe DSP 16. The flash memory 18 stores data which include plural sets ofcontrol parameters corresponding to the plural types of machine bodies1, mean movement spans S (to be described hereinlater in detail)corresponding to the plural types of machine bodies 1, a bias currentvalue Io to be described hereinlater and the like. These data items canbe rewritten through the personal computer 22.

FIG. 12 is a block diagram showing only a portion of the arrangement ofthe control unit 11 that is involved in the control of radial position.It is assumed that the pair of radial displacement sensors 7 shown inthe figure are, for example, disposed opposite to each other across therolling element 3 along X-axis. The outputs from these radialdisplacement sensors 7 are inputted to the sensor circuit 12 in which aprocessing is performed to subtract one of the outputs from the other.An output from the sensor circuit 12 is A/D converted for giving adisplacement signal ΔX. The signal indicates a displacement of therolling element 3 from a target position with respect to X-axis. The DSP16 outputs two exciting current signals (Io+Ic) and (Io−Ic) based on thedisplacement signal ΔX. Io means herein a bias current value, and Icmeans a control current value depending upon the sign and magnitude ofΔX. The exciting current signals (Io+Ic) and (Io−Ic) are each D/Aconverted and then amplified by an amplifier 13 a in themagnetic-bearing drive circuit 13. The amplified signals are supplied tothe pair of radial magnetic bearings 5 opposing each other across therolling element 3 along X-axis. According to the displacement signal ΔX,adjustment is made to the electromagnetic force with respect to adirection in which the displacement is reduced to 0. As a result. therolling element 3 is supported at the X-axis target position.

A similar positional control is performed on Y-axis.

FIG. 13 is a block diagram showing only a portion of the arrangement ofthe control unit 11 that is involved in the control of axial position.An output from the axial displacement sensor 6 is inputted to the sensorcircuit 12. Based on the output signal from the axial displacementsensor 6, the sensor circuit 12 determines a displacement of the rollingelement 3 with respect to a Z-axis target position. This displacement isA/D converted to a displacement signal ΔZ which is inputted to the DSP16. The DSP 16 outputs two exciting current signals (Io+Ic) and (Io−Ic)based on the displacement signal ΔZ. Io means herein a bias currentvalue, and Ic means a control current value depending upon the sign andmagnitude of ΔZ. The exciting current signals (Io+Ic) and (Io−Ic) areeach D/A converted and then amplified by the amplifier 13 a in themagnetic-bearing drive circuit 13. The amplified signals are supplied tothe axial magnetic bearings 4 disposed above and below the flangedportion 3 a of the rolling element 3. Based on the displacement signalΔZ, adjustment is made to the electromagnetic force with respect to adirection in which the displacement is reduced to 0. As a result, therolling element 3 is supported at the Z-axis target position.

The controllable magnetic bearing apparatus of the above arrangementconstitutes means for performing the rotation control and the positionalcontrol of the rolling element 3. Furthermore, the controllable magneticbearing apparatus also constitutes: means which, at the start ofoperation, uses a positional control function centralized on the DSP 16to move the rolling element 3 in a stationary state in a predetermineddirection for determining an amount of movement thereof to a movementlimit; and means which determines the machine type of magnetic bearing(machine body 1) based on the determined amount of movement for settingcontrol parameters. An operation for determining the machine type willhereinbelow be described in detail.

In the above controllable magnetic bearing apparatus, the axial magneticbearing 4, radial magnetic bearing 5 and motor 8 are not driven when thecontrol unit 11 is not powered up. Therefore, the rolling element 3 isat rest as supported by the protective bearings 9 in contact fashion.Upon power-up of the control unit 11, the DSP 16 identifies the machinebody 1 according to a flow chart of FIG. 1. The embodiment assumes thatthere are three types of machine bodies 1 which include Type-A, Type-Band Type-C. The length of the clearance between the rolling element 3and the protective bearing 9 varies with each machine type.

First in Step S1, the DSP 16 takes measurement of the amount of movementto the movement limit. Specifically, the DSP reads provisional controlparameters from the flash memory 18 to drive the axial magnetic bearings4. This allows the rolling element 3 to be magnetically levitated to aprovisional target position on Z-axis. In this state, the rollingelement 3 is allowed to move in the radial direction within the rangedefined by the inside-diameter circle of the protective bearing 9.

FIG. 2 to FIG. 6 are diagrams illustrating in plan the positionalrelationship between an inside-diameter circle C of the protectivebearing 9 and the rolling element 3 movable within an inscribed range ofthe circle. First assume as an initial state that the rolling element 3is positioned concentrically with the inside-diameter circle C, as shownin FIG. 2. In this state, the DSP 16 stores a displacement signalΔY0(=0) based on outputs from the radial displacement sensors 7 disposedin the +Y and −Y directions. Subsequently, the DSP 16 supplies apredetermined exciting current only to the radial magnetic bearing 5 inthe +Y direction to thereby attract the rolling element 3 in the +Ydirection. This brings the rolling element 3 into internal contact withthe +Y side of the protective bearing 9 (the inside-diameter circle C)(a state of FIG. 3). In this state, the DSP 16 reads a displacementsignal ΔY1 based on outputs from the radial displacement sensors 7disposed in the +Y and −Y directions. The DSP 16 calculates a difference(ΔY1−ΔY0) between the displacement signal ΔY1 and the previously storeddisplacement signal ΔY0. Additionally, the DSP 16 determines an amountYLp (of positive sign) of movement of the rolling element 3 moved in the+Y direction from the position of FIG. 2 to that of FIG. 3 using apreviously inputted corresponding relationship between the displacementsignal and the actual displacement, and then stores the amount ofmovement thus determined. Furthermore, the DSP 16 stores a displacementsignal ΔX0(=0) based on outputs from the radial displacement sensors 7disposed in the +X and −X directions.

Next, the DSP 16 supplies a predetermined exciting current only to theradial magnetic bearing 5 in the +X direction to thereby attract therolling element 3 in the +X direction. This brings the rolling element 3into internal contact with the +X side of the protective bearing 9 (theinside-diameter circle C) (a state of FIG. 4). In this state, the DSP 16reads a displacement signal ΔX1 based on outputs from the radialdisplacement sensors 7 disposed in the +X and −X directions. The DSP 16calculates a difference (ΔX1−ΔX0) between the displacement signal ΔX1and the previously stored displacement signal ΔX0. Based on thecalculation result, the DSP 16 determines an amount XLp (of positivesign) of movement of the rolling element 3 moved in the +X directionfrom the position of FIG. 3 to that of FIG. 4, then storing the amountof movement thus determined.

Next, the DSP 16 supplies a predetermined exciting current only to theradial magnetic bearing 5 in the −Y direction to thereby attract therolling element 3 in the −Y direction. This brings the rolling element 3into internal contact with the −Y side of the protective bearing 9 (theinside-diameter circle C) (a state of FIG. 5). In this state, the DSP 16reads a displacement signal ΔY2 based on outputs from the radialdisplacement sensors 7 disposed in the +Y and −Y directions. The DSP 16calculates a difference (ΔY2−ΔY0) between the displacement signal ΔY2and the previously stored displacement signal ΔY0. Based on thecalculation result, the DSP 16 determines an amount YLn (of negativesign) of movement of the rolling element 3 moved in the −Y directionfrom the position of FIG. 2 to that of FIG. 5, then storing the amountof movement thus determined.

Next, the DSP 16 supplies a predetermined exciting current only to theradial magnetic bearing 5 in the −X direction to thereby attract therolling element 3 in the −X direction. This brings the rolling element 3into internal contact with the −X side of the protective bearing 9 (theinside-diameter circle C) (a state of FIG. 6). In this state, the DSP 16reads a displacement signal ΔX2 based on outputs from the radialdisplacement sensors 7 disposed in the +X and −X directions. The DSP 16calculates a difference (ΔX2−ΔX0) between the displacement signal ΔX2and the previously stored displacement signal ΔX0. Based on thecalculation result, the DSP 16 determines an amount XLn (of negativesign) of movement of the rolling element 3 moved in the −X directionfrom the position of FIG. 3 to that of FIG. 6, then storing the amountof movement thus determined.

FIG. 7 is a plot of positions P0, P1, P2, P3 and P4 of the center of therolling element 3 moved from the state of FIG. 2 in the aforementionedmanner or in the order of FIG. 3, FIG. 4, FIG. 5 and FIG. 6 asmaintained in internal contact with the protective bearing 9. It isnoted that the aforementioned amounts of movement YLp, XLp, YLn, and XLnare such lengths as shown in FIG. 7.

It is noted that the initial position P0 of the center of the rollingelement 3 is not always at the center of P1 to P4, as shown in FIG. 8.In this case, YLp and YLn are not equal to each other because they areread with reference to the displacement signal ΔY0 with respect to P0.Even in this case, however, the center of the rolling element 3 is movedto the position of P1 when the rolling element 3 is attracted by theradial magnetic bearing 5 in the +Y direction. Accordingly, the amountsof movement, XLp and XLn are the same as in the case shown in FIG. 7.

Based on the amounts of movement, YLp, XLp, YLn and XLn thus determined,the DSP 16 calculates a mean value of movement span S (Step S2).Specifically, movement spans Ys and Xs in the Y and X directions arefirst determined using:

Ys=YLp−YLn

Xs=XLp−XLn

Next, the mean value of movement span S is determined using:

S=(Ys+Xs)/2  (1)

The reliability of the determination of the machine type (describedlater) is enhanced by determining the mean value S with respect to boththe X and Y directions.

Subsequently, the DSP 16 determines whether or not the mean value ofmovement span S satisfies:

S 1min≦S≦S 1max  (2)

where S1min and S1max denote a minimum value and a maximum value of theradial clearance between the protective bearing 9 and the rollingelement 3 in the machine body 1 of Type-A (Step S3). If the machine body1 is Type-A, the answer to the above expression (2) is YES. Therefore,the DSP 16 proceeds to Step S7 to read in control parameters for Type-Afrom the flash memory 18 and to set, based on the read controlparameters, target values of support for the axial magnetic bearings 4and the radial magnetic bearings 5.

If the machine body 1 is not Type-A, then the answer to the aboveexpression (2) is NO. Therefore, the DSP 16 proceeds to Step S4 todetermine whether or not the mean value of the movement span Ssatisfies:

S 2min≦S≦S 2max  (3)

where S2min and S2max denote a minimum value and a maximum value of theradial clearance between the protective bearing 9 and the rollingelement 3 in the machine body 1 of Type-B (provided that S1max<S2min).If the machine body 1 is Type-B, the answer to the above expression (3)is YES. Therefore, the DSP 16 proceeds to Step S8 to read in controlparameters for Type-B from the flash memory 18 and to set, based on thecontrol parameters, target values of support for the axial magneticbearings 4 and the radial magnetic bearings 5.

If the machine body 1 is not Type-B, the answer to the above expression(3) is NO. Therefore, the DSP 16 proceeds to Step S5 to determinewhether or not the mean value of the movement span S satisfies:

S 3min≦S≦S 3max  (4)

where S3min and S3max denote a minimum value and a maximum value of theradial clearance between the protective bearing 9 and the rollingelement 3 in the machine body 1 of Type-C (provided that S2max<S3min).If the machine body 1 is Type-C, the answer to the above expression (4)is YES. Therefore, the DSP 16 proceeds to Step S9 to read in controlparameters for Type-C from the flash memory 18 and to set, based on thecontrol parameters, target values of support for the axial magneticbearings 4 and the radial magnetic bearings 5.

If the machine body 1 is not Type-C, the answer to the above expression(4) is NO. Accordingly, the machine body 1 is not any of Type-A, Type-Band Type-C, so that the determination of machine type cannot be made.Therefore, the DSP 16 proceeds to Step S6 to indicate abnormality.

In this manner, the type of machine body 1 can be determined from themean value of the movement spans S, and thereby the setting of controlparameters for an applicable machine type is automatically made forquickly transferring the rolling element to a magnetically levitatedstate. Thus, the common control unit 11 makes it possible toautomatically set appropriate control parameters for any of the pluraltypes of machine bodies 1 and to control the position of the rollingelement 3. This permits the control unit 11 to be applied to generalpurposes, so that the control unit 11 can be mass-produced for achievingthe cost reduction. It is noted that abnormality is indicated only whenthe automatic determination is impossible and then an operator sets thecontrol parameters based on his determination.

Although the flow chart (FIG. 1) of the foregoing embodiment illustratesthe processing for selecting any one of the three types, it is alsopossible to make determination as to the larger number of machine typesfor automatic setting of the control parameters.

Although the foregoing embodiment determines the machine type based onthe amounts of movement YLp, XLp, YLn and XLn, it is also possible todetermine the machine type based on only the amount of movement in the Ydirection or X direction.

In the foregoing embodiment, prior to the determination of the amountsof movement YLp, XLp, YLn and XLn, the axial magnetic bearings 4 areexcited to effect a provisional state where the rolling element islevitated in the axial direction. However, the rolling element 3 may notbe axially levitated if the rolling element 3 can be axially attractedeven in a state where the rolling element is in contact with theprotective bearings 9.

In the foregoing embodiment, the determination of the machine type ismade based on the amount of movement to the movement limit in the radialdirection. However, it is also possible to determine the machine typebased on the amount of movement to the movement limit in the axialdirection. In this case, the rolling element 3 in a stationary state islevitated to bring its axial end portion 3 a into abutment against theprotective bearing 9 so that an amount of movement may be determinedfrom an amount of variation of the displacement signal ΔZ from the axialdisplacement sensor 6 and then the machine type is determined based onthis amount of movement.

What is claimed is:
 1. A controllable magnetic bearing apparatus sensinga position of a rolling element supported by a magnetic bearing andcontrolling the position thereof, the apparatus comprising: means formoving said rolling element in a stationary state in a predetermineddirection to determine an amount of movement thereof to a movementlimit; and means for determining a machine type of the magnetic bearingbased on said amount of movement and setting control parameters.
 2. Acontrollable magnetic bearing apparatus sensing a position of a rollingelement supported by a magnetic bearing and controlling the positionthereof, the apparatus comprising: means for moving said rolling elementin a stationary state in plural directions to determine respectiveamounts of movement thereof to respective movement limits; means fordetermining a mean amount of movement based on said amounts of movement;and means for determining a machine type of the magnetic bearing basedon the mean amount of movement and setting control parameters.
 3. Amethod for determining a machine type of a magnetic bearing comprisingthe steps of: moving a rolling element supported by a magnetic bearingfrom a rest position to place on one side of a first radial axis anddetermining an amount of movement thereof to a movement limit; thenmoving said rolling element to place on one side of a second radial axisand determining an amount of movement thereof to a movement limit; thenmoving said rolling element to place on the other side of the firstradial axis and determining an amount of movement thereof to a movementlimit; then moving said rolling element to place on the other side ofthe second radial axis and determining an amount of movement thereof toa movement limit; operating a mean amount of movement based on saidamounts of movement; and determining a machine type of the magneticbearing based on said mean amount of movement and setting controlparameters.